Debilitating infections due to Cryptosporidium parvum in AIDS patients are primarily the result of the continued unchecked recycling of type I meront and autoinfective sporont stages. The logarithmic multiplication of type I merozoites undoubtedly contributes most significantly to the overwhelming infection in these patients. Unfortunately, there are presently no effective chemotherapeutic agents available to combat this infection. Evidence has emerged, however, to suggest that stage specific or cross reactive antibodies, including monoclonals, may be useful in abrogating such infections. The main objective of this continuation project, therefore, will be to continue work on identifying and characterizing individual and pooled MAbs derived from merozoites which when used in conjunction with MAbs to the sporozoite stage may display optimal neutralization efficacy against C. parvum. Specific approaches to be taken to accomplish this objective will include: 1) optimizing the in vitro cultivation system for C. parvum development using Caco-2 cells to permit a) the large scale isolation of merozoites for neutralization assays, epitope characterization and mRNA isolation, b) the quantitative assessment of merozoite neutralization, and c) the development of C. parvum by determining a) individual and appropriate combinations of stage-specific or stage-cross reactive Mabs which will neutralize merozoites in vitro and b) antigen/epitope specificity of appropriate neutralizing MAbs. Pursuit of these objectives should help define optimal strategies for preventing or treating C. parvum infections in AIDS patients.